MOSCOW — Russia’s Defense Ministry says two officers died and three servicemen were hospitalized after cleaning rocket fuel tanks at a military launchpad.

The ministry said Tuesday that the officers appeared to have violated safety rules during the regular cleaning of the fuel tanks at the Plesetsk Cosmodrome in northwestern Russia.

The three servicemen were hospitalized after breathing toxic nitrogen vapors on Saturday and their lives were not in danger, the ministry said in a statement. It did not specify how the officers died.

The Plesetsk Cosmodrome is the only launchpad on Russian territory and is used mainly for sending up military satellites. Russia uses the Baikonur Cosmodrome, which it leases from Kazakhstan, for all manned space launches.